This invention relates generally to wind turbines, and more specifically to methods and apparatus for wind turbine braking.
At least some known wind turbines may include redundant braking systems to satisfy safety requirements. For example, at least some known wind turbines include a disk brake to facilitate stopping a wind turbine rotor against full wind torque, and a stored energy source, such as hydraulic accumulators, stored spring energy, capacitors, and/or batteries, to enable braking during a power failure. Moreover, at least some known wind turbines also include a braking system that aerodynamically brakes the rotor by pitching the rotor blades into a feathered position. Such braking systems may also include a stored energy source to enable the rotor blades to be pitched during a power failure. However, pitching the rotor blades into a feathered position to aerodynamically brake the rotor may induce vibrational stresses or other forces into the wind turbine and/or its associated components, such as a tower, that may damage such components and/or cause such components to fail. Moreover, at least some known wind turbines pitch the rotor blades into the feathered position at a constant rate that facilitates decreasing rotor speed as quickly as possible. However, such a constant rate of change of the pitch angle may increase an amount or severity of such vibrational stresses or other forces induced into the wind turbine and/or its associated components.